EL34 push pull DIY project

Submitted by costas sarris on Thu, 28/08/2008 - 12:00.

DIY Tube amps

EL34 amp project by Giannis Spathopoulos

This is Giannis Spathopoulos EL34 amp push pull diy latest project. It is a classic push pull amp design .

It is an ultra linear mode PP amp uses the EF86 (voltage gain) and the 6FQ7 (phase splitter )tubes at the driving stage. The output transformers are hand made (P&K audio). We build this amp in a ready-made chassis.It is all hard wired using silver Teflon cables in all critical paths. Listening this amp our first impression was very good. It has really excellent performance.

After some testings we publish the first draft schematic. Note that we apply no feedback at all. The plate-to-plate loading of the output stage is 5k Ohms and, the line voltage is 430 Volts. The Bias applied voltage is -47Volts ( -35V grid).
Input sensitivity measured at 1kHz is about 7.5 mV for an output of approximately 25 W with no feedback. Total harmonic distortion is about 1% when no feedback is applied.

Measurements and , data will be available soon.
We continue testing it and listening to it performing the necessary fine tuning.

Find a similar project by clicking here

Giannis Spathopoulos
el34-amp-schematic

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Hello, As drawn above on

Submitted by Marcus Wilson (not verified) on Mon, 27/04/2009 - 01:43.

Hello,

As drawn above on your webpage the phase splitter in the EL34 amplifier would not work. The 6FQ7 lowest in the drawing has an earthed grid (as far as audio is concerned) and the cathode is earthed through 100Kohms, so it has no signal input. The amplifier will still operate but at a lower power as one EL34 is not driven. My guess is that the cathodes of the two 6FQ7 sections should be linked.

regards,
Marcus.

its a classic long tail pair

Submitted by primbech (not verified) on Thu, 11/06/2009 - 03:11.

its a classic long tail pair set up for a singal polarity power supply ie the second grid is grounded for audio via the cap to earth the grids are linked via the 1M resistor

balance is acheved by the valuses of the two plae resitors being different , I cant see the values but 100 and 82 k would be typical

it will work ok

Am I Stupid?(probably) I

Submitted by lordbarclay (not verified) on Sun, 16/08/2009 - 10:36.

Am I Stupid?(probably)
I don't see any phase split in this circuit.
Is it done at the opt?
How can this be push pull?
Please enlighten me!
R.

6FQ7 is the splitter costas

Submitted by costas sarris on Fri, 28/08/2009 - 14:03.

6FQ7 is the splitter

costas

Im linking this for my

Submitted by torneos poker (not verified) on Wed, 02/09/2009 - 02:15.

Im linking this for my friend, he is going crazy about this projects, personally i dont have any idea about whats going on here, buut he seems very interested and your articles likes him a lot.

Good post, keep up the good

Submitted by Self Storage Manchester (not verified) on Wed, 02/09/2009 - 09:26.

Good post, keep up the good work:）

The first post is correct:

Submitted by Anonymous (not verified) on Mon, 15/03/2010 - 19:03.

The first post is correct: the phase splitter is disabled in the circuit diagram as shown. If instead the cathodes are tied together (or optionally linked by resistors) along with a current source (or another resistor) going to ground, the phase splitter is restored. But in the diagram as shown, the lower 6FQ7 sees no signal, as the first poster *correctly* points out.

Hello everybody.... I am

Submitted by andy (not verified) on Sat, 19/06/2010 - 17:25.

Hello everybody....

I am Wandi, from Indonesia.

Now a daily of my activity is in AM 80M Homebrew comunication.
I used 807 2paralel in final, 6L6 in Driver, 6V6 in Osc(VFO)
But I can get only 50W with 600V.

As per transistor transmitter I saw that many cicuit for PushPull...
Please help me for provide schematic PushPull 2x807..
For AM 80M band 3.5 - 3.7 Mhz..
That can get power 100W.

Everybody can help me please send me schematic
for 807pushpull power transmitter to my adress:
deswandi@gmail.com

I really hopr it..

Thankyouverymuch

Yes, it looks like a 'long

Submitted by lcelectro (not verified) on Sat, 31/07/2010 - 20:22.

Yes, it looks like a 'long tail pair', except that it is not and of course it won't work unless you tie the cathodes together. So, probably it's just a mistake in the drawing, otherwise you won't get much more than 15 W with one undriven grid at the output. (YES, I did the math) It's going to be better than a single tube output, as the tied together cathodes of the output tubes do some 'phase splitting' and it may operate as a class A push pull. (not much on the 15R resistor)
For the still-in-doubt, you can check: http://en.wikipedia.org/wiki/Valve_audio_amplifier_%E2%80%93_technical
http://www.mif.pg.gda.pl/homepages/frank/sheets/129/e/EL34.pdf
Regards, Luis.